Prognostics is the process of predicting system health and system failure. The word “prognostics” is similar to “diagnostics”, in that both refer to identification of a failure mode or a failed component responsible for abnormal behavior. Diagnostics typically occurs after the failure, or symptoms of failure, have already occurred (also sometimes called “fault isolation”). Prognostics differs from diagnostics at least in that prognostics determines what failure mode will likely occur in the future, or what component is starting to fail.
An aspect of prognostics is estimation of a system's life cycle and its remaining life. This allows the system user time to prepare and possibly prevent system failures. However, the prognosis of the life cycle of a system is difficult. Systems (e.g., turbofans) of the exact same build (e.g., identical brand/model), can have different life-cycles. Often, one turbofan can last more than twice as long as another turbofan. This can make life-cycle prediction difficult because the life cycle of a physical system is not just a function of time.